One of my players has created a Sikh Granthi as his character, but we're not sure how to handle languages. The London Investigators' Guide says "Granthis speak Punjabi and this does not count as one of their skills" (this also applies to Imams and Rabbis with Arabic and Hebrew, respectively). But what does this actually mean?

My interpretation is that it means that the character is bilingual and automatically gets both English and Punjabi at a starting skill equal to the investigator's EDU, without having to spend any points in character creation. Is this correct? Or does the character have to spend skill points on one of the languages?

Depending upon his actual origin country I'd either have Punjabi as his Native language (EDU% or EDUx5%) and English as Other Language or vice versa. One of them is going to have to have points spent on it . Attempts to get around skill point distribution are up to the Keeper and I'd squash any attempt to get 'free' points in this way. Anyone who want's to be bilingual as a way around the plot without paying for it is suspect.